The invention generally relates to internal combustion engines. More specifically, the invention relates to fuels, lubricants and additives. Another aspect of the invention generally relates to combustion and more specifically to processes of combustion operation, especially to feeding a flame modifying additive. Specifically disclosed is a method for providing and maintaining a catalytically active surface on combustion-exposed parts of an internal combustion engine, such as fire deck, valve faces and piston faces, so that combustion efficiency is improved and harmful exhaust emissions are reduced. The invention is particularly applicable to improving combustion in xe2x80x9cgreenxe2x80x9d engines, such as engines that are new, recently rebuilt, or that have low operating hours.
Worldwide emphasis on reducing global warming and reducing pollution mandates improved efficiency in combustion processes, which can be defined as improved fuel efficiency coupled with reduced emission of pollutants such as oxides of nitrogen (NOx). Ferrocene is known to improve combustion efficiency in burners, for example from U.S. Pat. No. 3,341,311. In quantitative terms, it has been reported that ferrocene can produce a 10% improvement in fuel efficiency. However, such results have not been uniformly achieved, especially with modern design, low emission engines, both new and after they have been in service for an extended time. Such modern engines, i.e., newer than 1995, are designed and constructed to consume less lube oil. In addition, they use cleaner fuels, lower in aromatic and sulfur content. All of these factors combine to minimize combustion chamber deposits. While modern engines running on modern fuels emit fewer pollutants than older engines, the technology has compromised the effective use of ferrocene to achieve still greater improvements.
In older literature, ferrocene was tested in diesel engines and showed effectiveness as a fuel additive for conditioning the engines to achieve improved fuel economy and reduced emissions. U.S. Pat. No. 4,389,220 to Kracklauer discloses a two-stage method of conditioning a diesel engine, resulting in reduced pollutant emissions and increased efficiency in fuel combustion. According to this patent, an initial high dosage of ferrocene, such as 20-30 ppm, in the diesel fuel can eliminate carbon deposits from the combustion chambers and deposit a layer of catalytic iron oxide on the combustion surfaces. Thereafter, a lower dosage of ferrocene, such as 10-15 ppm, maintains the catalytic iron oxide coating. It is considered undesirable to maintain the initial high concentration of ferrocene in diesel fuel, as this will lead to detrimental combustion modifications, minimizing or eliminating the beneficial effects of the catalytic iron oxide wall coating.
Older literature also shows that ferrocene can be effective in gasoline engines by improving the octane rating of treated fuel. In this way, ferrocene can reduce certain exhaust emissions and decrease fuel consumption in gasoline powered vehicles. Schug, K. P., Guttann, H. J., Preuss, A. W., and Schadlich, K., Effects of Ferrocene as a Gasoline Additive on Exhaust Emissions and Fuel Consumption of Catalyst Equipped Vehicles, SAE Technical Paper Series, 1990, paper number 900154. The method disclosed in this article and in related U.S. Pat. No. 4,955,331 is the simple addition of ferrocene to fuel as a method of achieving improvements in efficiency and emissions. This technology recently was tested with a modern engine using modern fuels. The test vehicle was a 1998 Dodge Intrepid with 29,500 miles on the odometer before testing started. Three fuel fills without ferrocene, corresponding to over 882 miles of operation, yielded a 27.7 mpg average fuel efficiency. Subsequently, four fills with ferrocene treatment, corresponding to 1170 miles, yielded a 26.4 mpg efficiency. These results suggest that simple addition of ferrocene to fuel as taught by Schug et al is not an effective method of improving combustion in such a gasoline fueled modern engine.
Other tests show that ferrocene does not produce combustion improvement in every case, especially when an engine is of modern design. A recent test with a 1998 Detroit Diesel Series 60 engine followed the process of U.S. Pat. No. 4,389,220 after the engine had accumulated 350 hours of break-in operation. Specifically, the engine was operated for 5 hours at a 125 ppmw dose of ferrocene to the fuel, followed by switching to a 25 ppmw dose for emissions testing. The test results showed no change in the fuel efficiency or NOx emissions of the engine. Hence, the simple staged addition of ferrocene to fuel as disclosed in U.S. Pat. No. 4,389,220 was not effective to improve performance of this modern design diesel engine.
Another approach to improved combustion is by the catalytic coating of combustion chambers prior to assembly and operation of the engine. In work described in Gaffney et al. xe2x80x9cSoot Reduction in Diesel Engines: A Chemical Approach,xe2x80x9d a diesel combustion chamber coated with platinum demonstrated a 40% particulate emission reduction. Unfortunately, this combustion catalytic effect was fully lost after 50 hours of normal engine operation.
Siegia and Plee, xe2x80x9cHeterogeneous Catalysis in the Diesel Combustion Chamber,xe2x80x9d attempted to duplicate Gaffney""s result with a new engine having a platinum coating. However, no catalytic activity of any kind was found, despite use of the same platinum coating. This series of experiments showed two of four unresolved problems with platinum coatings: 1) the catalytic effects are non durable; and 2) the catalytic effects are not reproducible. The remaining two unresolved problems with platinum are high cost and the toxicity of platinum as an exhaust pollutant, itself.
Other ferrocene related technology is disclosed in U.S. Pat. No. 4,612,880 to Brass et al., which discloses a method of controlling octane requirement increase in internal combustion engines. This method requires introduction of a gasoline soluble iron compound such as dicyclopentadienyl iron (ferrocene) together with a carboxylic acid or ester derivative thereof, into a combustion chamber coated with alumina or zirconia with a carbon gassification catalyst dispersed therein. However, this technology involving base metal surface catalysis is not effective for the process of this invention, as shown in the test reported at Table 1, 5b2 of this document. In addition, the disclosed catalyst compositions are prepared from soap or salt precursors and used in thick coatings, which deteriorate combustion efficiency.
SAE Paper 910461 discloses a thermal barrier coating that produces increased combustion efficiency of 1.7%. An undesirable effect of this thermal burner coating is an increase in NOx output, which is unacceptable in modern engines facing severe emission control constraints.
It would be desirable to provide improved combustion efficiency by a method or coating that can be made effective even when an engine is xe2x80x9cgreen,xe2x80x9d or has few operating hours, such that the combustion surfaces have not yet developed substantial combustion deposits.
Similarly, it would be desirable to provide the previously known benefits of ferrocene usage in engines of modern design, i.e., post 1995, having low consumption of lube oil and adapted to use modern fuels with lower aromatic and sulfur contents.
Further, it would be desirable to develop a durable or maintainable coating for the combustion chamber that can maintain the combustion facing surfaces at catalytically active temperatures, despite the attachment of the durable insulating coating on the combustion facing surfaces to a coolant-cooled wall surface.
In combination with providing a catalytically active combustion chamber surface for improved combustion efficiency, it would be desirable to provide a device or system to continuously maintain the active nature of the surface.
To achieve the foregoing and other objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, the method of this invention may comprise the following.
Against the described background, it is therefore a general object of the invention to provide an improved, reliable and durable, catalytically active film on the combustion facing surfaces of a combustion chamber, such as the fire deck, valve faces and piston faces, in order to improve combustion, even when an engine is xe2x80x9cgreen,xe2x80x9d has few prior operating hours, is of a design allowing reduced consumption of lube oil, or uses cleaner fuels of lower aromatic and sulur content.
A related object is to provide a method of forming or depositing an improved, catalytically active film on the combustion facing surfaces of a combustion chamber, such as the fire deck, valve faces and piston faces, in order to improve combustion.
Another object is to provide a catalytically active surface and method of forming such surface in a combustion chamber that is capable of maintaining a temperature in the catalytically active range despite the connection of the combustion facing surfaces to a coolant cooled wall surface, which may be at temperatures below 320xc2x0 C.
Still another object is to provide a method to incorporate into or on to a combustion facing surface of a thermally insulating coating a catalytically active metal, which is active in carbon particulate and fuel oxidation at catalytically active surface temperatures.
An important object is to provide an effective method and system for delivering a maintenance dosage of a catalyst precursor in the combustion charge to each cylinder so that the catalytic activity of an existing catalyst is continuously maintained and refreshed.
Additional objects, advantages and novel features of the invention shall be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by the practice of the invention. The object and the advantages of the invention may be realized and attained by means of the instrumentalities and in combinations particularly pointed out in the appended claims.
According to the method of this invention, improved combustion is achieved in an internal combustion engine of the type igniting a combustion charge in an area having a combustion facing engine surface. The method provides the initial step of applying to a combustion facing engine surface a substrate layer of high thermal inertia. This initial step is performed in either of two ways: a substrate precursor may be supplied in the combustion charge during engine operation; or a thermal barrier coating may be supplied on the combustion facing engine surface prior to engine assembly. Simultaneously or subsequenty to the initial step, a further step of the method provides a catalyst surface on the substrate layer. This catalyst surface is of the type active in carbon particulate and hydrocarbon oxidation at a surface temperature of at least 450xc2x0 C. In a next step of the method, during operation of the internal combustion engine and subsequent to the step of providing the catalyst surface, a maintenance dosage of a catalyst precursor is provided in the combustion charge to the catalyst surface on a substantially continuous basis during stable engine operation. Thus, catalytic activity is substantially continuously maintained.
In the method, the internal combustion engine may be either a compression ignition engine or a spark ignition engine. The substrate layer is of a material having a surface area of 300 to 500 meters per gram as measured by BET nitrogen absorption. It may be of 100 to 100,000 angstroms thickness and is preferred to be a film of less than 0.1 mm thickness. The preferred substrate layer is selected from zirconia, silica, and lube oil ash.
According to the method, the substrate may be formed of a thermal insulating compound effective in providing a high thermal inertia to the catalytic surface to maintain it in a catalytically active temperature region during stable engine operation. The thermal insulating compound may be of the type effective to maintain the catalyst surface at a temperature of at least 450xc2x0 C. during stable engine operation.
The method provides that the catalyst surface may be selected from nanophase iron, nanophase platinum, and combinations of the two. The catalyst surface may be created during operation of the engine by supplying a combustion charge containing ferrocene in an effective dosage to establish a catalytic iron coating. This combustion charge may contain ferrocene in a dosage range from 25 to 120 ppmw of engine fuel. The step of providing the catalyst surface may be performed simultaneously with the step of providing the substrate layer. The catalyst precursor preferably is supplied in a dosage from 5 to 50 ppmw of engine fuel. The catalyst precursor may be ferrocene. The ferrocene may be provided to the combustion chamber by adding it to the fuel or to lube oil, or by vaporization into the intake air to the engine.
The accompanying drawings, which are incorporated in and form a part of the specification illustrate preferred embodiments of the present invention, and together with the description, serve to explain the principles of the invention. In the drawings: